Japan’s second-largest mobile operator had disruptions to both voice calls and data communications over much of the weekend

This weekend saw Japanese operator KDDI suffer its largest network disruption ever, leaving almost 40 million customers without mobile services.
The disruption seemingly began in the early hours of Saturday morning, with disruption continuing to varying degrees until Monday morning. 
KDDI blamed “equipment failure” for the outage, saying staff were replacing a router for its core network as part of regular maintenance when an error prevented the connection of voice calls. While this situation was being resolved, KDDI said it experienced a high volume of traffic that further impacted service quality for customers.
The operator is still exploring exactly what caused the disruption. 
During the outage, KDDI advised customers to use landlines and public phones to access emergency communications. 
This fall-back solution is potentially a black mark against the new Japanese government, led by Kishida Fumio, which has been attempting to rapidly digitalise Japan over the last year, including replacing landlines and public phone boxes with more advanced technology. 
This transition to digital technology and retirement of legacy, analogue solutions something that is taking place all over the developed world and, in some cases, is proving similarly problematic. In the UK, for example, BT came under fire earlier this year for the removal of public phone boxes and landlines when a storm caused an outage of their mobile network and thus left thousands of customers unable to access emergency services. The UK operator has since paused its removal of landlines in rural areas, as it develops a more “resilient rollout” for these more vulnerable areas.
In comparison, the situation in Japan is unlikely to get quite so severe; new rules introduced by the Kishida administration will mean that public phone boxes must be deployed at least ever square kilometre in urban areas, and two square kilometres in rural areas, due to their reliability during natural disasters.
Nonetheless, the extent to which Japan is already heavily reliant on mobile communications was on full display during the outage, with disruptions not only impacting customers directly but also other services, like package delivery, weather reports, and cash machines, all of which could not function without mobile data transfer.
The Japanese government characterised the outage as “a severe incident”, with Deputy Chief Cabinet Secretary Seiji Kihara telling reporters he expected a full explanation from KDDI and potential compensation for severely affected customers. 
"It is extremely regrettable that mobile phone service, which is a crucial infrastructure for social and economic activity, has been unusable for such a long time,” he said.
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